Many land vehicles, such as cars and trucks, are shaped to exert a low wind drag when travelling. A specific problem is the influence of cross wind or side wind.
U.S. Pat. No. 5,379,218 ('218) concerns the influence of side wind on the steering of the vehicle. The arrangement described in '218 includes means for detecting side wind by differential pressure detection and is provided with means of two pressure sensors on each side of the vehicle. When side wind is detected, the arrangement of '218 automatically counteracts the effect on the steering by adjusting the steering based on the detected side wind, i.e. based on the determined pressure difference.
One further problem especially concerns trucks provided with trailers, which may suffer from a large drag due to the influence of side wind. Side wind may enter through gaps between the truck and trailer, and between trailer and ground respectively. This creates increased aerodynamic drag since the air interacts with components arranged on the undercarriage at the underside of the trailer, causing increased turbulence around the vehicle. Even if the truck is aerodynamically shaped for low drag, the underside of the trailer is vulnerable to wind influences and such influence is not counteracted by aerodynamic design of the truck alone.
US 2013/0270857 ('857) describes a side skirt wall for preventing air flow from entering under the chassis of a trailer. The side skirt wall is designed for reducing the air drag resulting from an air flow entering and interacting with the undercarriage components of the vehicle. The side skirt is attached to a lower edge of a side wall of the trailer.
US 2011/0148142 ('142) describes an aerodynamic device for a vehicle with trailer. The aerodynamic device provides side skirts (9 in '142) to the trailer and is provided with air ducts (15, 20, 22) for directing an air flow along the side wall of the side skirt towards the rear side of the trailer preventing drag-inducing whirls behind the vehicle. The aerodynamic device is attached to a lower edge of a trailer side wall.
Both the side skirts described in '857 and '142 provide reduced drag during side wind conditions, compared to a vehicle without side skirts.
However, due to the need for ground clearance of the trailer, the side skirts may not extend fully down to the surface of the road. A drawback with the side skirt systems described in '857 and '142 is therefore that, side wind may still enter in the space between the side skirts and the road surface.
US 2010/0201152 ('152) describes a side deflector assembly for reducing air drag of a vehicle that comprises a truck and a trailer, especially preventing side wind from entering a vertical gap between the truck and the trailer. The assembly comprises a control system that includes a side wind sensor to independently extend side deflectors arranged on opposing sides of the vehicle.
A drawback with the assembly of '152 is that the side deflectors extend laterally from the vehicle, making the vehicle wider. A wider vehicle may be a safety risk, for example to bypassing vehicles. Also, a further disadvantage with the assembly of '152 is that the side deflectors only prevents air from interfering with the front side of the trailer and does not prevent air from interfering with the undercarriage of the trailer.